Morphology and mortality of sporophytes resulting from intergametophytic and intragametophytic mating were studied in the fern Athyrium filix-femina. In a long-term experiment, we determined the relevance of heterosis and/or genetic load in this homosporous fern species. Progeny from intergametophytic crossing, probably consisting of heterozygous individuals, exhibited most vigorous growth, small morphological variation, and low mortality. Progeny resulting from intergametophytic selfing, likely to include individuals with various levels of homozygosity, showed larger morphological variation, higher mortality, and smaller mean leaf length. Progeny from intragametophytic selfing (completely homozygous) had the smallest mean leaf length, highest mortality, and considerable morphological variation. These results for a homosporous fern species agree with theoretical and empirical studies on heterosis and genetic load in flowering plants.